System for amplification of small currents



C. W. RICE.

SYSTEM FOR AMPLIFICATION OF SMALL CURRENTS APPLICATION FILED JULY 31,1917.

Patented Mar. 16, 1920.

Fig. 2

I Irwventor: heater" W. Rice UNITED STATES PATENT OFFICE.

CHESTER; W. RICE, OI F SCHENECTADY, NEW YORK, ASSIGNOB TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

I SYSTEM FOR AMPLIFICATION OF SMALL CUBRENTS.

Specification of Letters Patent.

Patented Mal-.16, 1920.

, Application filed July 81, 1917. Serial No. 183,786.

To all whom it may concern Be it known that I, CHESTER W. R ca, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful Improvements in Systems for Amplification of Small Currents, of

which the following is a specification. I My present invention relates to the amplification of electric currents of small intenclosed 'in'an evacuated envelop, for receiving radio signals.

It has been found that under certain conditions'a device of the above type produces oscillatory currents in the circuits associated therewith and in some cases the oscillatory currents so produced interfere with the efflcient reception, amplification and detection of the signals to be received.

The object of my invention is to .avoid the undesired production of oscillatory currents when such a device is used either as an amplifier or detector, or to serve both functions. A

It has been ascertained that the production of oscillatory currents by such a device is due to the coupling which is always present between the grid and plate circuits. This coupling is of two kinds, electromagnetic and electrostatic. When the plate and grid circuits both contain air core inductances which are not magnetically shielded from each other there will be a large leakage fiux between the two and electromagnetic transfer of energy from the plate circuit to the grid circuit which may be sufficient to produce oscillations in the circuits even though the coils .may be located at some distance from each other. There is in any case a certain electrostatic coupling between the two circuits by reason of the capacity between the electrodes and the capacities to ground of the circuits. This couplin alone ma also be sufiicient to produce oscil ations;

It as been proposed to neutralize the electromagnetic coupling by a second electromagnetic coupling in the op osite direction. ThlS coupling may also e made great enough to compensate for the capacity coupling but in case it is so arranged it will be correct only for one particular frequency and in case the tuning of either of the circuits is varied the degree of the coupling also will have to be varied.

in carrying my invention into effect I overcome the electromagnetic coupling between the circuits which is present when air core inductances are used by inclosing the inductances in separate metal boxes. I also overcome the effect of the electrostatic coupling by impressing upon the circuits electromotive forces equal to and opposite in dlrection to those impressed thereon by reason of the natural capacity coupling and thereby neutralize the effect of this coupling When this compensation is once ad- ]usted it is effective for all frequencies to which the circuits may be tuned.

The novel features which I believe to be characteristic of my invention are set forth withparticularity in the appended claims.

My invention itself however both as to its organization and method of operation together with further objects and advantages thereof will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 shows a simple radio receiving system to which my invention is applied, and Fig.2 shows a modification in which several electron discharge devices are connected in series relation.

As indicated in Fig. 1 the antenna 1 is grounded at 2 through the usual air core inductance 3. This inductance is coupled to the air core inductance 4 which is included in the tuned grid circuit of the amplifier .and detector 5. The circuit between the capacity between the grid 10 and anode 11,

which is represented by the dotted condenser 12, I apply to the grid circuit through the condenser 13 an electromotive force equal and opposite to that impressed, upon the event instead of connecting the battery 18 which supplies the plate circuit to one end of the coil 6, I connect, as indicated, to a point 19 intermediate the ends of the coil and thereby compensate for the effect of capacity between the two coils. The electromotive force impressed upon the grid circuit through the natural capacity coupling represented by condenser 16 will be equal and opposite in direction to that impressed on the grid circuit through the natural capacity coupling represented by condenser 17.

I have found that in some cases if the antenna is coupled to the coil 4 in the usual manner and a close coupling is used that the gradation in potential between the two ends of the coil 4 may upset the balance of the circuits sufficiently to produce oscillations. In such cases it may be found desirable to tune the antenna in phantom as indicated, the variable condenser 20 being connected to balance the natural capacity 21 of the antenna and the ground connection made to the central point 22 of coil 3. In this way two equal and opposing electromotive forces will be impressed upon coil 4 from the antenna and the balance will be maintained under all conditions.

My invention is especially adapted for use with the system for tuning in geometric progression described in U. S. Patent #1,173,079 to Ernst F. V. Alexander-son, and in Fig. 2 I have indicated a manner in which it may be employed in connection with that system. In this case a series of amplifiers having tuned grid and plate circuits are used to produce a SHCCGSSIVG amplification of the current received by the antenna. The battery 18 supplies current for the operation of the amplifiers 23. 24, and 25. The antenna 1 is connected to thegrid circuit of the first amplifier 23 in the same manner as described in connection with Fig. 1. The plate circuit of amplifier 23 is tuned by means of inductance 26 and capacity 27 to the frequency of the received signals, and the grid circuit of amplifier 24 is tuned by means of inductance 28 and capacity 29. The two circuits are coupled by inclosing inductances 26 and 28 in the same metal box 30 although an iron core transformer designed for radio frequency may be employed if desired. The plate circuit of amplifier 24 and the grid circuit of amplifier 25 are tuned and coupled in the same manner. The receiver 31 is inserted directly in the plate circuit of the amplifier 25.

In this case I .have omitted the condenser 13 and the connection in which it is included, as I have found that if coils having a large number of turns are employed, the capacity between the coils is so great in comparison with the capacity 12, that the effect of the latter may be neglected.

While I have shown and described only two modifications of my invention, I do not wish to be limited to the particular organizations illustrated, as it will be apparent that many modifications may be made in the precise connections employed without departing from the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. The combination in a radio receiving system of an electron discharge amplifier having resonant grid and plate circuits and capacity coupling between said circuits so arranged as to prevent the generation of 0scillatory currents in said circuits which in terfere with the reception of desired signals.

2. The combination in a radio receiving system of an electron discharge amplifier having grid and plate circuits containing inductances which are so arranged as to avoid any magnetic coupling between the two circuits and capacity coupling between said circuits so arranged as to prevent the generation of oscillatory currents in said circuits which interfere with the reception of desired signals.

The combination in a radio receiving system of an electron discharge amplifier having resonant grid and plate circuits containing inductances which are so arranged as to avoid any magnetic coupling between the two circuits. and capacity coupling between said circuits so arranged as to prevent the generation of oscillatory currents in said circuits which interfere with the reception of desired signals.

4. The combination in a radio receiving system of an electron discharge amplifier having grid and plate circuits, with natural capacity coupling between the circuits and containing inductances which are so arranged as to avoid any magnetic coupling between the two circuits, and means for impressing upon the grid circuit from the plate circuit through the natural capacity coupling between the two circuits two equal and opposing electromotive forces.

5. The combination in a radio receiving system of an electron discharge amplifier having grid and plate circuits with natural capacity coupling between the two circuits and means for impressing upon the grid circuit from the plate circuit through said natural capacity coupling two equal and opposing electromotive forces.

6. The combination in a radio receiving system of an electron discharge amplifier having grid and plate circuits containing inductances with natural capacity coupling between said inductances, and means for impressing upon the grid circuit from the plate circuit through said capacity coupling two equal and opposing electromotive forces.

7. The combination in a radio receiving system of an electron discharge amplifier having a cathode, a single anode and a single grid and having a resonant grid circuit, an inductance shunted by capacity, a connection between the cathode of said amplifier and the central point of said inductance and a connection between the anode of said amplifier and one end of said inductance.

8. The combination in a radio receiving system of an electron discharge amplifier having a cathode, an anode and a single grid and having a resonant plate circuit, an inductance shunted by capacity, a connection between the cathode of said amplifier and the central point of said inductance and a connection between the grid of said am plifier and one end of said inductance.

9. The combination in a radio receiving system of an electron discharge amplifier having a cathode, a single anode and a single grid and having resonant grid and plate circuits, an inductance in said grid circuit connected at its central point to the cathode of said amplifier and connected at one end to the grid of said amplifier, and an inductance in said plate circuit connected at its central point to the cathode of said amplifier and connected at one end to the anode of said mplifier.

10. The combination in a radio receiving system of an electron discharge amplifier having a cathode, an anode and a grid, and having a resonant grid circuit, a pair of inductances coupled to each other, a portion of one of said inductances being included in the grid circuit, a ground connection to the middle point of the second inductance, an antenna connected to one end of the second inductance, and a condenser connected between the other side ofsaid inductance and ground.

- 11. The combination in a radio receiving system of an electron discharge amplifier having a cathode, an anode and grid, and having a resonant plate circuit, an inductance shunted bycapacity, a connection between the cathode of said amplifier and the central point of said inductance, a connection between the grid of said amplifier and one end of said inductance, and means for impressing upon the two parts of said inductance from an antenna, two equal and opposing electromotive forces.

12. The combination in a radio receiving system of an electron discharge amplifier having a cathode, an anode and a grid, and having resonant grid and plate circuits, an

inductance in said plate circuit connected at its central point to the cathode of said amplifier and connected at one end to the anode of said amplifier, an inductance in said grid circuit connected at its central point to the cathode of said amplifier and connected at one end to the grid of said amplifier and an inductance coupled to said grid circuit inductance having its central point grounded, one end connected to an antenna and the other end connected to ground through a hand this 30th day of July, 1917.

CHESTER W. RICE. i 

